An illegal fighting pit in the flooded lower levels of a decommissioned water treatment plant in Waukegan, where fighters compete in waist-deep water and the rules are whatever the crowd decides they are. The venue holds maybe 200 spectators standing on elevated walkways above the flooded basin, looking down at two people trying to fight in conditions that make traditional technique almost useless. Striking is slow, grappling is slippery, and the water is cold enough that fights rarely last more than five minutes before hypothermia becomes a factor.

Undertow is run by a collective of Waukegan Shelf residents who discovered the flooded plant and saw an opportunity. Admission is 5 Quanta, fighters keep whatever the crowd throws in (literally — Quanta chips rain down into the water), and the event moves to a different section of the plant each week to avoid pattern detection by enforcement drones. The water fights have developed their own meta: successful fighters are usually swimmers or divers who understand how to move in water, and the reigning champion is a former lakefront lifeguard named Anika Petrov-Asante who has won fourteen consecutive bouts by holding opponents underwater until they submit.